The present disclosure relates to an image scanner and an image forming apparatus equipped with the image scanner, and more particularly to a technique of detecting that dew condensation occurs on a transparent member for placing a document thereon.
Heretofore, an image scanner has been configured to irradiate a document placed on a plate-shaped transparent member, with light from a light source, such as a fluorescent lamp or an LED, through the transparent member, and photoelectrically convert reflected light from the document by a photoelectric conversion element, thereby generating document image data as a scanned image of the document.
One example of a prior art document (hereinafter referred to as “prior art document 1”) discloses a technique of acquiring temporally-adjacent first and second shading data for shading correction, and, when a difference between the acquired two shading data is equal to or greater than a predetermined value, determining that dew-condensation occurs. Another example of the prior art document (hereinafter referred to as “prior art document 2”) discloses a technique of pre-storing, as a reference light value, an amount of reflected light from a standard white plate in a state free from the occurrence of dew condensation, and comparing an amount of actual reflected light from the standard white plate with the reference light value to determine whether or not dew condensation occurs.
However, in the technique disclosed in the prior art document 1, a dew condensation state during acquisition of the temporally-preceding first shading data is unknown, so that determination on the occurrence of dew condensation is likely to be erroneously made. Moreover, there is a problem that, in a process for the determination on the occurrence of dew condensation, a waiting time arises for a period of time after the acquisition of the first shading data through until the acquisition of the second shading data.
On the other hand, in the technique disclosed in the prior art document 2, an amount of reflected light from the standard white plate in the state free from the occurrence of dew condensation is pre-stored as a reference light value, so that determination on the occurrence of dew condensation is likely to be erroneously made due to a reduction in amount of reflected light from the standard white plate resulting from a reduction in amount of light from a light source caused by aging thereof, although no waiting time is required for the determination on the occurrence of dew condensation.
In view of the above circumstances, it is an object of the present disclosure to provide an image scanner and an image forming apparatus capable of determining the occurrence of dew condensation quickly and accurately even if a light source undergoes aging.